Lungworm

This image, taken under a microscope, shows a lungworm (Angiostrongylus vasorum) which was found in a dog’s faeces

In this article we focus on Angiostrongylus vasorum (A. vasorum) which is also known in the UK as ‘Lungworm’ or ‘French Heartworm’ (it was first documented in France in 1853). It is now found across most of Western Europe, with occasional cases reported in the USA, South America and Canada.

It is important to know that this is not the same as ‘dog Heartworm’ – Dirofilaria immitis – which is commonly found in the USA, Canada and South America, and also on the European continent. There are also other lungworm parasitic infections, such as Crenosoma vulpis (‘fox lungworm’), which will not be discussed in this article.

Is lungworm a problem in the UK?

Yes, unfortunately this parasite has become increasingly common in the UK over the past two decades. The south of England and Wales were originally the main hotspots, but there have now been reported cases as far north as Scotland.

Angiostrongylus vasorum mainly infects domestic dogs and foxes. However there have been reports of infections in wolves, coyotes, otters and ferrets. There have also been reports suggesting that foxes can act as a reservoir of infection for domestic dogs, and therefore areas with large populations of foxes may be more at risk of infection.

What type of parasite is Angiostrongylus vasorum?

Angiostrongylus vasorum is a ‘Nematode’ parasite. Nematodes are also known as round worms. Adults are approximately 14 – 20 mm in size, but the juvenile stages are not visible to the naked eye.

How can my dog become infected with lungworm?

Dogs can become infected with lungworm by eating infected snails

Slugs and snails act as intermediate hosts in the life cycle of Angiostrongylus vasorum and therefore dogs can become infected by eating them.

Dogs may also acquire infection through eating frogs and other amphibians (paratenic hosts).

It is also possible for the larvae (juvenile Angiostrongylus vasorum) to temporarily leave the host (eg. slugs or snails) and therefore dogs can potentially pick them up from their contaminated environment. For example by eating grass, drinking from puddles, playing with sticks or toys that are left in the garden overnight, especially when raining and wet.

What is the full life cycle of Angiostrongylus vasorum?

Inside the slugs and snails, Angiostrongylus vasorum is in a larval (juvenile) form, which is known as ‘L3’ or ‘third stage larvae’.

Once the animal has eaten L3, the larvae develop in the dog’s intestines and from there they migrate to the main artery in the lung and the right side of the heart. It is in these locations where the adults remain and can live for several years.

Once here, the female adult worms begin laying eggs from about 40 days after infection. The eggs then hatch rapidly, and larvae (‘L1’ or ‘1st stage larvae’) move into the lungs.

Once in the lungs the L1 larvae are coughed up and swallowed into the intestines, where they are passed in faeces.

The slugs and snails then become infected with L1 larvae by direct contact with the dog’s faeces. In the slugs or snails, the larvae develop from stage 1 (L1) to stage 3 (L3) which is then infectious to dogs, and the whole cycle starts again.

If an animal is not treated for lungworm, they can excrete L1 larvae for up to two years, or possibly longer if untreated.

Occasionally lungworm can be found in other locations such as the brain, bladder, kidney or eye. If here, this can result in different symptoms related to the invasion of, or bleeding within, these organs, such as seizures if in the brain.

There are many different and unrelated diseases that can cause similar signs and symptoms, however. Consultation and testing with your vet is recommended to confirm this parasitic infection as the cause.

How is lungworm infection diagnosed?

The ‘pre-patent period’ (the time between when the animal was infected to when the parasite can be detected) is approximately 4 to 8 weeks, occasionally up to 15 weeks.

There are four main ways that Angiostrongylus vasorum can be diagnosed by your vet, using samples of faeces, lung fluid or blood:

Baermann technique

Broncho-alveolar lavage

PCR test

ELISA test

All these tests can be negative, even though the dog is infected, for various reasons. These include the stage of the infection, the test’s accuracy and the type of sample being tested. A combination of tests may then be used by your vet to diagnose or exclude lungworm infection.

Can humans become infected with lungworm?

No. Angiostrongylus vasorum is not a zoonotic parasite, which means that it cannot be transmitted to humans.

How can I prevent my dog from becoming infected with lungworm?

Regular preventative therapy is recommended, especially in endemic areas, with an anti-parasitic medication that is effective against Angiostrongylus vasorum. It is important to discuss with your vet a parasite control programme that works best for you and your dog.

Picking up your dog’s faeces in your garden and in the local park, as this will prevent the spread of the parasite to other slugs and snails

Removing toys from the garden overnight so they are not exposed to slugs and snails. Slugs and snails are most active at night, especially in damp or wet conditions

If your dog’s water bowl is outside, ensure the water is changed regularly

Restrict or minimise drinking from puddles and general scavenging

Can lungworm infection be treated?

Yes, the same medications that are used to prevent lungworm can also be used for treatment. Successful and especially early treatment can lead to full recovery. If your dog is infected with Angiostrongylus vasorum it is important to discuss with your vet the best treatment plan.

Your vet may also prescribe other supportive treatment if required and rest is very important for your pet so they can recover (at least 2-3 days).

About Roger Powell

Roger is a clinical pathologist running PTDS, an independent veterinary diagnostic centre in Hertfordshire. He has both the British and American Diploma in Veterinary Clinical Pathology and fellowship of the Royal College of Pathologists. He consults with first opinion and referral vets, daily analysing samples from sick animals to help diagnose what is wrong with them, in order to allow them to be treated correctly.